1. Field of the Invention
The present invention relates to a shut-off system for a duct. Although not exclusively, it relates more specifically to a shut-off system for an orifice of an air inlet passage that allows air into the combustion chamber of a ramjet.
2. Related Art
It is known that ramjets consist essentially of a combustion chamber, ending in a jet nozzle and into which liquid or gaseous fuel (which may be obtained from a solid fuel) and combustion air are introduced. This combustion air is introduced into said combustion chamber through at least one air inlet passage, of the air scoop type, which picks up air when said ramjet (or the airborne body carrying it) moves with respect to the ambient air.
Thus, for a ramjet to work, it has first of all to get up to speed with respect to said ambient air.
To achieve this, it is customary, in an initial phase of operation corresponding to getting said ramjet up to speed, for the latter to be operated as a rocket, using a consumable auxiliary propellant arranged in said combustion chamber and then, when said ramjet has reached a predetermined speed and said auxiliary propellant has been completely consumed, operation switches to ramjet mode proper, with fuel and combustion air injected into the combustion chamber.
Such a dual-mode operation (rocket mode followed by ramjet mode) means that a shut-off system has to be provided for, on the one hand, shutting off an orifice in said air inlet passage or air scoop during rocket mode operation, so as to avoid gases generated by said consumable auxiliary propellant leaking through said orifice and so as, on the other hand, to open said orifice in the air inlet passage or air scoop for ramjet operation proper.
It is known practice (see for example document JP-03057867) to use, by way of a shut-off system, a controlled-opening pivoting flap. However, in this case, it is generally necessary to provide a particularly sophisticated control system, preventing any inadvertent opening of the flap which could lead to premature ignition of said consumable auxiliary propellant and therefore to damage to the carrier (aircraft for example) of a missile equipped with said ramjet. In addition, and above all, this flap remains present on board the ramjet after the air inlet passage has been opened, and this obviously poses problems of bulk and leads to the presence of an unwanted mass during ramjet operation.
To at least partially overcome this last disadvantage, document FR-2 474 594 describes a shut-off system for an inlet orifice allowing combustion air into the combustion chamber of a ramjet, which comprises:
a glass cover or shutter which completely shuts off said orifice during the initial phase; and
a destruction device, namely a mechanical percussion device, which destroys this glass shutter prior to ramjet operation. During this destruction, the glass shutter is broken up into small fragments. As the orifice is downstream of the air scoop and corresponds to the mouth into the combustion chamber, these fragments are ejected to the outside, backward, by passing through the combustion chamber and the jet nozzle.
In consequence, the shutter is completely eliminated during ramjet operation.
However, this known shut-off system has certain disadvantages. First of all, there is a risk of damaging the combustion chamber and the jet nozzle by the ejection of the glass fragments through these.
In addition, the use of a mechanical percussion device comprising, in particular, a piston and a striker ending in a spike, poses certain problems. Specifically:
either this percussion device acts frontally on the shutter, so as to be able to break it easily, in which case it is necessary to arrange the shutter in the air inlet passage which means that it disrupts the air flow during ramjet operation;
or the percussion device is arranged outside said air inlet passage, in which case it can act only sideways on the shutter, this reducing the effectiveness of this destruction device because it is far more difficult to break the glass, and especially to break it completely, from such a position.
It is an object of the present invention to overcome these drawbacks. The present invention relates to a shut-off system for an orifice of a duct, particularly for an orifice of an air inlet passage that allows air into the combustion chamber of a ramjet, and which makes it possible:
to open said orifice of the duct at a given moment in an effective and danger-free way, and
to completely uncover said duct once the orifice has been opened,
while at the same time alleviating the aforementioned problems of mass and bulk.
To this end, according to the invention, said shut-off system for a duct, of the type comprising:
a shutter capable of completely shutting off said orifice of the duct; and
a controllable actuating device capable of acting on said shutter to uncover said orifice, is notable in that said shutter comprises a removable cap which is held on said duct in such a way as to completely shut off said orifice and a locking device which keeps said cap on said duct by at least one locked jaw, which is unlockable, and in that said actuating device comprises at least one controllable striker means which is capable of unlocking said jaw in such a way as to cause the cap to be ejected from said duct and to uncover said orifice.
Thus, by virtue of the invention, said cap is ejected from the duct during unlocking, the duct is completely opened, this opening being achieved without any danger to the duct or to the elements arranged therein or near it.
In addition, said shut-off system is simple and inexpensive to produce.
Furthermore, as said cap is removable and is simply held on the duct, it is not necessary, in order to implement the present invention, to design said duct in a special way. In consequence, the present invention can be applied to any type of existing duct.
Furthermore, by virtue of said striker means, unlocking can be achieved very effectively, as will be seen in greater detail hereinbelow.
Advantageously, said striker means acts on a trap which can move under the action of said striker means.
In addition, advantageously, said trap comprises an elastic buffer to damp the action of said striker means, which makes it possible to obtain a soft impact with the trap, such a soft impact making it possible to conserve the corresponding momentum while at the same time protecting the trap and the mechanical elements associated with it.
Furthermore, advantageously, said locking device comprises:
at least one tightening means which is capable of tightening said jaw onto the duct so as to lock it and which is capable of being moved in such a way as to unlock said jaw; and/or
at least one attachment in the form of a loop, which can collaborate with a base in the form of a hook, which is fixed to the outer face of the duct.
In a preferred embodiment, said striker means comprises:
at least one projectile which is capable of moving said trap when it is projected into the latter; and
a controllable projection means capable of projecting said projectile and which is arranged outside said duct while at the same time being oriented in such a way as to be able to project said projectile into said trap.
Thus, by virtue of the invention:
as the projection means is arranged outside the duct, it does not impede the air flow once the orifice has been opened (in ramjet mode for example), said duct being completely open; and
as the striker means comprises the projection of a projectile, it is possible to actuate said trap and thus eject said cap in spite of the remoteness of the projection means and of the fact that it is arranged outside said duct.
In addition, by virtue of said trap, the projectile is caught and presents no danger to elements or people in the vicinity of said duct.
To optimize the precision with which the projectile impacts the trap and thus improve the effectiveness of the unlocking, the shut-off system according to the invention advantageously additionally comprises a straight guide for guiding said projectile, which straight guide is produced in the form of a canal, one end of which faces said projection means and the other end of which is directed toward said trap.
As a preference, said striker means comprises a pyrotechnic striker. This may be the striker means proper, or may be the projection means.
Furthermore, advantageously, said cap comprises an outer face which is inclined with respect to a predetermined direction that represents flow of fluid outside the duct. This makes it easier for the cap to be separated (or ejected) from said duct, when said cap is unlocked, because of the action exerted by said fluid flow on said inclined outer face.
It will be noted that the shut-off system according to the invention can be implemented on various types of duct, the opening or uncovering of which needs to be performed in the operating environment. In addition, it is able to withstand very severe mechanical, thermal, vibrational and electromagnetic stresses.
In a preferred application, the shut-off system according to the invention is intended to shut off an orifice of an inlet passage for introducing combustion air into the combustion chamber of a ramjet, said ramjet being capable, in a known way, in an initial phase of operation corresponding to said ramjet getting up to speed, of operating as a rocket by virtue of a consumable auxiliary propellant arranged in said combustion chamber and then, when said ramjet reaches a predetermined speed, of operating as a ramjet proper with fuel and combustion air injected into said combustion chamber, and said shut-off system comprising, in a known way:
at least one shutter capable of completely shutting off said orifice during said initial phase of operation of the rocket; and
at least one controllable actuating device capable of acting on said shutter so as to open said orifice for operation as a ramjet.
According to the invention, said shut-off system is notable in that, in addition to the aforementioned characteristics (regarding the actuating device and the shutter), said shutter shuts off the inlet orifice in the air inlet passage upstream of the latter in the direction of flow of the air in said air inlet passage.
Thus, the cap is ejected (a great distance away) from said air inlet passage, without entering the latter. In consequence, by virtue of the invention:
on the one hand, unlike a conventional pivoting flap which remains on the ramjet after opening, an advantageous reduction in mass and bulk is achieved; and
on the other hand, unlike a known glass shutter, the fragments of which pass through the combustion chamber and the jet nozzle, there is no risk of damage to said ramjet.
The present invention relates also to a ramjet equipped with a shut-off system like the aforementioned one, and to a missile comprising such a ramjet.